1. Field of the Invention
This invention relates generally to digital communication systems. In particular, this invention relates to an electronic memory circuit for storing a serial stream of digital data which does not require the use of a battery power system.
2. Description of the Prior Art
Telemetry systems are used to provide digital data on missile performance during flight with the digital data being provided by a radio frequency data link consisting of a missile telemetry transmitter and a ground, aircraft or ship board telemetry receiving system. The missile telemetry transmitter modulates the missile data which is then transmitted in free space and received, recorded and processed by the receiving system whether authorized or unauthorized. Unauthorized reception of this data can provide an intercepter with technical information relating to the missile's performance. This missile performance data may be then used to develop effective countermeasures to the missile.
Thus, there is a need for a secured communications system to protect missile performance data during transmission. Secured communications systems, such as the systems described in U.S. Pat. Nos. 4,392,241 and 4,563,546, generally use an encryption circuit which scrambles the digital data prior to transmission so that the true information content of the digital data is not revealed during transmission.
Generally, encryption circuits such as the Model KGV-68 encryption circuit manufactured by Motorola and the enciphering device described in U.S. Pat. No. 4,563,546 receive a digital/key word which initiates the scrambling of the digital data to hide its true information. The digital or key words, in turn, are often stored for lengthy periods of time in a battery backed Random Access Memory (RAM) storage system.
However, the batteries utilized are often large due to high current drain needed to operate the Random Access Memory and associated voltage sensing circuits. In addition, the high amperage hour batteries utilized with the battery backed RAM are often dangerous due to the batteries caustic chemicals. Thus, it can readily be seen that there is a need for a digital memory storage device for use aboard missiles which does not require battery power.
Therefore, it is an object of the present invention to provide a memory circuit for storing digital data for lengthy periods of time which does not require backup batteries.
It is a further object of the present invention to provide a memory circuit which is small in size since there is limited space on board a missile.
Yet another object of the present invention is to provide a memory system which can store digital data for a period of time of approximately three years.
Another object of the present invention is to provide a memory system which is compatible with encryption circuits.
These and other objects, advantages and novel features of the invention will become apparent from the following description of the invention when considered in conjunction with the accompanying drawings.